Koi eating water lettuce.

[big ron]

I have had water lettuce in my pond all summer to help with the algae and for shade and it has done a great job for keeping the water clear.  My koi did not fool with it all summer.  It grew to a point that I had to remove a 5 gal bucket every other day which was no problem. However in the past 2 weeks they have completely destroyed it to a point it is almost gone.  My question is, why would they now decide to eat it when all summer they did not touch it ? Is it because they were not getting enough to eat.  They eat like pigs.  Also , is there any floating plant that will control algae that they will not bother ?   Thanks for your help 

[miguynmkoi]

I've never been able to keep any plants with free exposed roots in the same pond as the koi.  They don't really eat them as much as try to rip everything apart.  I have a bog in a waterplant pot off to the shallow sides of my pond to prevent big lips from the roots.  Just a couple of weeks ago I had to thin out the plants because the koi were literally pulling the leaves off the taro and irises.